Flexible shafts comprise basic elements of power transmission and are designed to transmit power or control from a driving element to an element to be driven. Transmission may be over, under, or around obstacles or objects where transmission by solid shafts would be impractical or impossible.
In a typical rotatable flexible shaft, a wire mandrel has a plurality of layers of closely coiled wire wound thereover, each of the layers being successively wound over another in alternately opposing directions, i.e., right or left-hand lay. This shaft is usually covered by a flexible casing, metallic or covered, and a clearance between the shaft and casing is provided in order that the shaft may rotate freely within the casing.
Rotatable flexible shafts are of two basic types--power driven and remotely,controlled. Power driven flexible shafts are designed primarily for motor-driven or high speed operation in one direction. Remote control flexible shafts, on the other hand, are designed primarily for hand-operated control, usually 100 rpm or less, or intermittent high speed use, in either direction of rotation.
Torsional deflection is measured in degrees per foot of shaft per pound-inch of load and is determined by torsionally loading the shaft with various load increments and measuring degrees of twist resulting therefrom.
In most remote control applications, a minimum amount of torsional deflection, or "lag", between the control and controlled element is permissible, regardless of the direction of rotation of the shaft. It is virtually impossible to entirely eliminate torsional deflection, unless solid shafts are employed, because of the alternate layers of wires either winding or unwinding when the shaft is subjected to the torsional load. Regardless of the direction of rotation of the flexible shaft, it should operate smoothly and be free of any tendency to "jump".
In a typical remote control application where a manually-operated steering wheel controls a remotely disposed rudder or other steering member on a marine vessel, it is desirable that rotation of the steering wheel offer the same degree of resistance in either direction of rotation, and not feel "spongier" when rotated in the "unwind" direction. Similarly, other elements driven by rotatable flexible shafts in response to remotely controlled hand-operated wheels, valves, knobs, and the like, will benefit from the practice of the present invention.